1. Field of the Invention
The present invention relates to a rack type electric power steering apparatus. More particularly, it relates to a rack type electric power steering apparatus in which the tensional force of a belt becomes higher as the distance between a motor shaft and a rack bar becomes larger because a second inclined portion of a support body passing through a guide hole is moved upwards along a first inclined portion to be inserted into a coupling recess, and accordingly, noise and damage to the belt can be prevented. Further, if the support body is inserted into a coupling recess by a third inclined portion of a coupling recess and a motor housing is moved upwards, the tensional force of the belt becomes higher as the distance between the motor shaft and the rack bar becomes larger, and accordingly, noise and damage to the belt can be prevented.
2. Description of the Prior Art
In general, a steering apparatus refers an apparatus that allows the driver to rotate a steering wheel to freely change the direction of travel of a vehicle, and is an apparatus that arbitrarily changes the center of rotation about which the front wheels are pivoted to help the driver drive the vehicle in a desired direction.
FIG. 1 is a partially sectional view of a rack type electric power steering apparatus according to the related art.
As illustrated in FIG. 1, the rack type electric steering apparatus, according to the related art, includes a rack bar 109 that extends in a transverse direction of a vehicle and has a rack gear part on one side of an outer peripheral surface thereof, a pinion shaft 104 that has a pinion gear part that is engaged with the rack gear part, a ball screw part 150 that has balls 201, a ball screw 203, and a ball nut 205 engaged with the ball screw 203 via the balls 201, a belt type transmission unit 140 that connects the ball nut 205 and a motor shaft 221, a motor 130, and a motor housing 240 that is fixed to a rack housing 223 through bolt coupling while surrounding the motor 130.
The pinion shaft 104 is connected to a steering wheel through a steering shaft, and the rack bar 109 that has a screw of a predetermined length on one side of an outer surface thereof is installed within the rack housing 223.
The ball screw part 150 includes a ball nut 205, which is coaxially formed with the rack bar 109 and surrounds the rack bar 109, and the balls 201 that make contact with the ball screw 203 formed on the outer surface of the rack bar 109.
The ball nut 205 is rotated together with the motor shaft 221 as the motor shaft 221 is rotated, and a bearing 207 is provided between an outer peripheral surface of the ball nut 205 and an inner peripheral surface of the rack housing 223 for the smooth rotation of the ball nut 205.
The belt type transmission unit 140 includes a belt 230 that connects the motor shaft 221 and the ball nut 205, and transmits auxiliary power that is generated by the motor 130 to the rack bar 109 through the ball nut 205 in proportion to a steering torque applied to the steering wheel.
That is, as the motor shaft 221 is rotated, the ball nut 205, which received a rotational force of the motor shaft 221 through the belt 230, is also rotated, and as the ball nut 205 is rotated, the rack bar 109 is axially linearly moved according to the movements of the balls 201 and the ball screw 203.
FIG. 2 is a side view of a motor housing and a rack housing of the rack type electric power steering apparatus according to the related art.
The motor 130 is fixed by coupling the motor housing 240 surrounding the motor 130 and the rack housing 223 by means of bolts 270.
If the motor shaft 221 drives the belt 230 while being rotated to rotate the ball nut 205 during a steering operation, a force that pulls the motor shaft 221 and a shaft of the rack bar 109 including the ball nut 205 towards each other is applied by a tensional force of the belt 230.
Because the generated force is concentrated on a coupling portion of the bolts of the motor housing 240 and the rack housing 223, which is most mechanically vulnerable, and the motor shaft 221 is moved towards the rack bar 109 that includes the ball nut 205 by a phenomenon in which the bolts 300 are released due to vibration and an impact occurring while the motor shaft 221 is rotated during a steering operation, the tensional force of the belt 230 decreases, noise occurs between the belt 230 and a driving pulley 280 or a driven pulley 290, and the belt 230 is damaged.